Kabuto is TRULY UNDERRATED on the Naruto power scale.
Kabuto is undoubtedly a top 10 most powerful character in the series before the Six Paths characters.
Not only does the story make this quite clear, but within what the fandom can argue regarding his power, there are very few characters who can compete against Kabuto when he's at 100%.
Whether you like it or not, Kabuto IS a character on par with Kakashi in Part 1, meaning a high-level jonin who can approach Kage levels... this is verifiable in his very first important fight in the series when he defeats Tsunade, who, although nerfed, is still a Sannin and a Kage-level ninja.
By the time he gets his modifications, it's almost obvious that Kabuto ranks above all the Sannin by a considerable margin and is more powerful than characters like Itachi or Pain. Starting with the fact that he possesses:
• Quasi-immortality on par with Orochimaru
• The ability to absorb bodies just like Orochimaru
• Even superior regeneration thanks to Karin and Suigetsu's DNA
• His Sage Mode is of indefinite or infinite duration
• He has a sound-based Genjutsu against which neither the EMS nor a Genjutsu genius like Itachi could easily escape
• He can combine all the abilities of the Sound Five, even those he doesn't appear capable of using (the databook confirms that he has all the techniques of the people from whom he absorbed DNA). This means: Bone hardening like Kimimaro, Kidomaru's steel-like durability, Jirobo's chakra absorption jutsu, and the ability to duplicate his cells in other people's bodies like Ukon and Sakon.
• Manda 2.0 is more powerful than the original Manda, which in turn must be stronger than Gamabunta and Katsuyu. A creature physically capable of competing with Tailed Beasts.
• Invulnerability to visual Genjutsu.
And of course, the most important ability of all, which is completely forgotten when discussing Kabuto's power: the Edo Tensei.
All of Kabuto's reanimated corpses are part of his arsenal and an extension of his true power. Some Edo Tensei are powerful enough to rival the Five Kage.
Allowing him to use the Edo Tensei in battle, he should be the most powerful character in the ninja world who isn't a Six Paths character.